Does the away goals rule make your brain keel over and give you something extra to panic about ahead of a crucial Socceroos match? You're not alone.
For regular football fans, especially those who follow competitions like the UEFA Champions League and Europa League, away goal calculations are second nature.
But to those who value their sleep and won't be found watching Round of 32 penalty shoot-outs between Hoffenheim and Slavia Prague at the crack of sparrows, it's a metric than can trip punters up.
The Socceroos face Honduras in the second leg of the intercontinental World Cup qualifying play-off tonight in Sydney, having drawn the first leg 0-0 at San Pedro Sula last Saturday morning.
Here's how the tie is poised, and how that pesky away goals rule could come to the fore.
So what do the Socceroos need to do tonight?
For those that are time poor, the answer is simple: Australia must win the second leg to go through to the World Cup, either in 90 minutes, in extra time or in a penalty shoot-out.
Be it 1-0, 2-1, 5-3, or whatever winning score line you can imagine, that's how Australia is qualifying for Russia 2018.
The only way the game can go to extra time is if it is still 0-0 after 90 minutes. Only a goal-less draw will see the match go to extra time; no other score line will do.
So how does Honduras progress?
Well, they too will go through if they win outright in 90 minutes, extra time or via penalties. But the Central American team has one more ace up its sleeve that Australia does not, and that's away goals.
Australia's only chance to notch an away goal or two came in the first leg, and that was spurned in a 0-0 draw.
Honduras has the chance to cause some carnage by scoring a goal (or three) in Sydney in the second leg. If the scores are level after 90 minutes (aka 'a score draw') at 1-1, 2-2, 3-3, etc, then Honduras goes through on the away goals rule.
A hypothetical: The match ends at 2-2 after 90 minutes. The aggregate score, when you 'add in' the 0-0 from the first leg, is also 2-2. The deciding factor is away goals, and Australia would have zero, while Honduras would have two.
So Honduras would qualify, and Australia's campaign would end in disaster.
Hang on, don't away goals 'count double'?
No, that's often bandied about but it's more a figure of speech.
The phrase is mentioned in FIFA's Rules of the Game. Under the section 'Procedures to determine the winner of a match or home-and-away', it states:
"Competition rules may provide that where teams play each other home and away, if the scores are equal after the second match, any goals scored at the ground of the opposing team will count double."
But this can confuse casual fans. Does that mean if Australia lead 2-1 after 90 minutes, it's really 2-2 on aggregate?
Simply, no. If Australia wins 2-1, it wins the two-legged tie 2-1 on aggregate. Away goals 'counting double' is a bit of a misnomer. It really means that only after a tie ends with the scores level, suddenly the away goals are more valuable.
Again, if goals are scored and the aggregate score is level at full time, Honduras will have more away goals than Australia and will go through.
But what if it's 0-0, it goes to extra time, and then both teams score?
The away goals rule carries over into extra time as well.
If by the end of 120 minutes the scores are locked in a score draw, again, Honduras goes through on away goals. There isn't suddenly an away goals amnesty just because an extra 30 minutes have been tacked on to the match.
So how will the Socceroos approach the match?
Defensively, Australia will be looking to shut up shop, as Honduras looked to do on its turf last Saturday. The away goals rule in both club and international football has, down the years, seen home teams play more defensively to avoid conceding a potentially crippling away goal.
In this case, the return of Mark Milligan will certainly help shoring up our midfield, either as a starter or from the bench, given how well Mile Jedinak performed alongside Massimo Luongo in the first leg.
But Australia certainly needs to score and will want to have the job done in 90 minutes, before tired legs and crazy nerves come to the fore in extra time.
The inclusion of Robbie Kruse and Matthew Leckie will certainly spice things up going forward, while you can probably expect Tom Rogic to start in place of Jackson Irvine.
And of course, there's Tim Cahill, who didn't play any minutes in San Pedro Sula, and will be itching to create some history on home turf.
Coach Ange Postecoglou could throw the Socceroos legend up front, or he could persist with Juric, who at least knows how to find a way to goal in front of home fans.
